Plotline

The Enterprise receives a garbled signal from the Cepheus system. Whilst investigating, the crew are paralysed by a mysterious energy discharge. Afterwards they find that all organic matter on the ship is shrinking! Kirk finds a colony of miniature Humans on the surface of the planet, which is being threatened by the conditions there.

Analysis

This is an episode where the makers use the real benefit of animation - there is no way TOS would have been able to show the Enterprise crew shrinking, the FX technology of the time simply wasn't up to it. It's amusing watching the ever-smaller crew trying to operate the Enterprise by pushing oversized buttons, though you have to wonder why they couldn't just set up a voice interface when things began to get a bit out of hand. The basic plot doesn't make a lot of sense though - why don't the Terratins just explain their situation and ask for help in the first place, and why is Kirk reluctant to help them later on? Because it serves the script, that's why not.